Abstract: Take outdoor unit condenser of air conditioning on the roof of a restaurant generates high decibel noise during operation, exceeding the standard noise value of 18.54 dB as an example. A composite sound insulation hood which can meet the noise reduction value of the condenser is designed, and the reverberation chamber method is used to verify that the designed sound insulation hood can meet the noise reduction requirements. As the outer structure of sound insulation cover is the key factor restricting the cost, the outer structure of sound insulation cover is optimized according to the optimization design theory, and the optimal size parameters of sound insulation cover are obtained as 2 000 mm long, 1 492 mm wide and 2 011 mm high. At the same time, through the modal analysis of the structure of the sound insulation hood, the first six orders of vibration pattern and natural frequency of the sound insulation hood are obtained. It is found that the first six orders of natural frequency can avoid the operating frequency of the condenser, so as to avoid the occurrence of resonance.